Adipose tissue growth and development can be described as an orderly sequence in which cell number is developed early in life and maintained constant thereafter. Cell size on the other hand remains more flexible. An "adipose cell hypothesis" has been elaborated which states that obesity can be a disorder of both cell number development as well as hypothesized controls linking cell size and energy metabolism. Various aspects of this hypothesis are being tested in animals. The technique of lipectomy, or surgical removal of fat, performed at various times in development is being used as a tool to examine the proliferative capacity of adipose tissue as it changes from early life to adulthood. Adipose tissue cellularity and studies of DNA turnover in adipocytes have been essential additions to these studies to permit a full and critical evaluation of the results. A study of the effect of lipectomy on adipose mass and cellularity with and without various nutritional modifications so as to enlarge or contract the adipose depot, is being undertaken to provide a definitive evaluation of the degree to which adipocyte size can exert effects on food intake.